Articular cartilage normally serves as a wear resistant, low friction, load- bearing surface in diarthrodial joints. However, during aging and osteoarthritic cartilage degeneration in adult humans, biomechanical properties deteriorate. The long-term goal of this project is to elucidate the cellular and molecular basis for the biomechanical dysfunction of human articular cartilage during "aging" and "osteoarthritis", and also to develop diagnostic assays of this dysfunction. During the current grant period, we found that articular cartilage (1) has (a) compressive and tensile moduli that vary markedly with depth from the articular surface, (b) tensile properties that diminish modestly with normal aging (defined by gross morphology and histopathology) in a site-specific manner in adult humans, and (c) properties that appear dependent on both fixed charge and collagen network properties, (2) becomes more brittle with controlled aging by in vitro glycation, (3) has marked increases in intrinsic fluorescence during aging that needs to be accounted for in assessing DNA content, and (4)allows attachment of exogenous cells in a time-dependent manner. We now propose to further analyze the extent and mechanisms of biomechanical dysfunction in adult human articular cartilage during "aging" and "osteoarthritis". In particular, we propose the following. (1) To expand the biomechanical analysis of depth-dependent properties of human articular cartilage to osteoarthritic tissue in order to assess how both "aging" and "osteoarthritis" each contribute to altered material and structural mechanical properties, (2) To determine if distinct matrix metabolic pathways of "aging" and "osteoarthritis" are evident in human cartilage, as well as cartilage treated in vitro, and contribute to altered biomechanical properties. (3) To determine if cell density, organization, and phenotype are altered in "aging" and "osteoarthritis", as well as cartilage treated in vitro, and also contribute to altered biomechanical properties. Elucidation of depth-varying tissue-scale properties of cartilage are critical to an overall understanding of cartilage biomechanical function. Determination of the sensitivity of structural biomechanical testing in specific regions of human articular cartilage will help evaluate a diagnostic modality. Elucidation of mechanistic pathways leading to cartilage biomechanical dysfunction in aging and osteoarthritis may ultimately suggest therapeutic interventions.